Only react to touches on the uiOverlay that hit a subview.

Why this isn't the default, I'll never know. It has caused an endless series of headaches for mdb
and myself, with the touches getting transformed on the way to PlayN graphics. I have tested for
a rotated landscape device (and it starts in portrait), but I have not tested on a system that uses
the pixel doubling for ipad tech. MDB, would you please do the honors?

If this change works out, I believe the touchScale is no longer needed.

This change is spurred on by my next change: selective masking of the uiOverlay. I've broken those
changes into another commit because I think they might be controversary in their own way and I want
these two bits to be considered seperately.
Stub out a more formal system for UI overlays.

In TriplePlay, a Java overlay was recently added that will be moved up here after a bit more
work. The real driver for this though, is to make it possible for non-platform-specific code to
tell whatever overlay might be there to get the hell out of the way and allow some specific
rectangle on the GL stack to bleed through.

The only implementor currently is iOS. It is potentially possible that this could support (at least
for iOS) more complicated shapes, but this was already complicated enough; let's just go with rects
for now.
It ends up not mattering here, but this is the correct usage.
Shortcut the masking op when area didn't change.